1. Field of the Invention
This invention relates to a memory addressing scheme suitable for convolutional interleaver and de-interleaver configurations used, e.g., in digital television (DTV) data transmission and reception.
2. Discussion of the Known Art
Noise frequently causes bit errors in digital data transmission systems. To detect and correct such bit errors, several different error correction techniques are known. Interleaving is one method especially effective to cure errors induced by noise bursts, wherein a large number of adjacent bits of a data bit stream may be affected.
An interleaver rearranges the order of data bytes in an original data stream before transmission, by re-locating a certain number of adjacent bytes in the stream according to a defined interleave pattern. At the receiving end, a de-interleaver restores the order of the received data bytes, to obtain the original order of the bytes in the data bit stream.
A recently defined digital television or "DTV" standard for the Unites States prescribes convolutional interleaving to protect broadcast DTV data from noise bursts when the data is transmitted over long distances from a transmitter site to a DTV receiver site. The standard states:
"The interleaver employed in the VSB [vestigial sideband] transmission system shall be a 52 data segment (intersegment) convolutional byte interleaver. Interleaving is provided to a depth of about 1/6 of a data field (4 ms deep). Only data bytes shall be interleaved. The interleaver shall be synchronized to the first data byte of the data field. Intrasegment interleaving is also performed for the benefit of the trellis coding process." Advanced Television Systems Committee (ATSC) Document A/53, Section 4.2.4. The prescribed convolutional interleaver is shown in FIG. 6 of ATSC doc. A/53, and is reproduced in FIG. 1 of the present disclosure. PA1 "The convolutional de-interleaver performs the exact inverse function of the transmitter convolutional interleaver. Its 1/6 data field depth, and intersegment "dispersion" properties allow noise bursts lasting about 193 microseconds to be handled. Even strong NTSC co-channel signals passing through the NTSC rejection filter, and creating short bursts due to NTSC vertical edges, are reliably handled due to the interleaving and RS [Reed-Solomon] coding process. The de-interleaver uses Data Field Sync for synchronizing to the first data byte of the data field." The prescribed de-interleaver is shown in FIG. 10.14 of ATSC doc. A/54 and is reproduced in FIG. 2 of the present disclosure.
A data de-interleaver is described in ATSC Document A/54. Section 10.2.3.10 of doc. A/54 states:
All relevant portions of both ATSC Documents A/53 and A/54 are incorporated by reference herein.
As seen in FIGS. 1 and 2, a typical convolutional interleaver/de-interleaver for accommodating the DTV standard, requires 51 branches each comprised of a different number of byte shift registers. The known approach requires 51 independent counters to keep track of I/O addresses for each branch, an 8-bit wide 52.times.1 input de-multiplexer, an 8-bit wide 52.times.1 output multiplexer, and the required I/O selection circuitry. This approach thus requires a relatively large amount of hardware.
U.S. Pat. No. 5,572,532 (Nov. 5, 1996) discloses a convolutional de-interleaver for DTV data, including an address signal generator for repeatedly generating sequences of address signals for a de-interleaving random access memory (RAM). See also U.S. Pat. No. 5,241,563 (Aug. 31, 1993) and U.S. Pat. No. 5,537,420 (Jul. 16, 1996).